Herbaceous clematis: choosing and growing the best herbaceous clematis

By Daniel Griffiths

Published: Thursday, 28 April 2022 at 12:00 am

What are herbaceous clematis?

Trends, flowers and colours may divide our tastes in the gardening community but very few plants have the universal admiration and enduring popularity of the much-loved clematis. The plants have such wide-ranging appeal, originating from a broad and diverse group of nearly 300 species. The genus Clematis has been planted and cultivated in English gardens since the 16th century and belongs to the Ranunculaceae or the buttercup family, alongside border stalwarts such as delphiniums, anemones and thalictrums.

Every family has its divas and if we put the large-flowered – and, dare I say, temperamental – attention-seekers to one side for a moment, I would like to explore the easier-to-grow, generously flowering and endlessly rewarding herbaceous group.

Lacking tendrils to cling as they climb, these clematis need support, and will happily scramble through either a birch or a hazel-clad dome, or through a neighbouring shrub.

The shrub Physocarpus opulifolius ‘Diabolo’, for example, is a useful, rich-purple foil for other plants, but now let’s imagine it with the violet-blue flowers of Clematis ‘Arabella’, popping all over its foliage, and suddenly it has been elevated to another level of interest entirely.

These gorgeous, herbaceous clematis offer us an easy win – simple to look after and care for, extending the season of our shrubs and borders, and flowering late on into the mist-filled autumn. All they ask of us is a few pea sticks or a shrub through which to scramble. I don’t think that’s a bad deal at all.

IN BRIEF

What Herbaceous clematis, including non-twining, climbing species and hybrids bred from species such as C. integrifolia, C. x diversifolia, C. viticella, C. heracleifolia, C. recta and C. viorna. Sometimes known as solitary or entire-leaved clematis.
Origins Originating from Europe and Asia.
Season Long-lived plants with an extensive flowering period from midsummer to early autumn.
Size From 60cm-2.5m in height with a 50cm-1m spread, depending on the species.
Conditions Tolerant of most fertile garden soils that do not become waterlogged or dry out. Best grown in full sun or light shade with a cool root run. Will grow on a range of pH, but particularly suited to neutral or alkaline soils.
Pruning group Pruning group 3 (remove previous year’s growth to a pair of strong buds in late winter).
Hardiness Hardy throughout all of UK and northern Europe with an hardiness rating of RHS H4 to H6. Depending on species they are suitable for gardens in USDA zones 3a-9b.

How to grow herbaceous clematis

How to plant herbaceous clematis

The advice of keeping the tops sunny and the base cool may be crude, but it is very apt for growing the majority of clematis. If fertile, moist and free- draining soil frustratingly eludes you, why not try growing clematis in a container? A good-sized, deep pot is ideal, filled with a mixture of peat-free compost and John Innes No.2, say 50:50, with a few handfuls of grit. Just add a 5cm layer of grit on the top and a fortnightly potash feed during the growing season and you’ll have a winning formula.

Pruning herbaceous clematis

Clematis pruning can baffle and may deter some from growing these plants but the unadulterated joy that characterises this selection of clematis is that their treatment could not be simpler: as they flower on their current year’s growth, they need to be cut down to just above the ground each spring as their buds begin to swell.

Propagating herbaceous clematis

If you are looking for an exact replica of your plant, division, cuttings or layering techniques are at your disposal, but a number of these species are easy to grow from seed. Clematis seed does not keep for long so it’s best sown when ripe and comes away from the plant with ease.

Sow thinly on top of a pot full of compost (2-3cm off the rim) and cover lightly with more compost before topping with a layer of grit to hold the moisture in and protect the seed. Place in a cool spot and do not allow the seeds to dry out. Do not be too quick to throw the pot away if germination isn’t swift, as they can be erratic. And remember that patience is a virtue.

Herbaceous clematis problems

Clematis wilt strikes fear into the hearts of most gardeners, but rest assured that the herbaceous group, with their refined and sophisticated flowers, are rarely affected.

Aphids can be problematic when growth begins in spring, but if you’re on the ball these can easily be dealt with through physical removal or a garlic- or soap-based spray.

Rabbits find young clematis shoots very appetising, so if they are a problem for you, protect the young shoots with some chicken wire and remove when the growth matures and the allure subsides as the stems harden.

Slugs and snails can also be tempted by the young leaves, and damage by these hungry pests will delay flowering and weaken the plant. A very knowledgeable chap once told me to control slugs and snails in February to prevent subsequent populations booming. Half an eaten grapefruit, turned upside down, or a beer trap from late winter onwards should keep them at bay without the need for pellets.

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The best herbaceous clematis for your garden

Clematis ‘Alionushka’

A free-flowering herbaceous clematis with deep-mauve to pink, bell-shaped flowers from early summer right through to the autumn. An excellent form for growing up a trellis or wall, but remember to help the plant out by tying it in as it grows.

1.5m. AGM*. RHS H6.